Do I need to spend a lot of money on equipment?

To start with - no, however try to buy a boat in reasonably good condition. This will reduce the maintenance in your first year(s) of competing. A solid composite boat will cost between £200 and £400, a good pair of paddles around £100 in pretty good condition.

You can use your current whitewater kit, and replace with more race oriented kit when it wears out (and you get more enthusiastic!).

The second hand market is very strong for wildwater racers, so resale value on a new boat is pretty good.